Peanuts in various product forms are recognized as nutritious and palatable snacks by consumers in all age groups. Actually, their high calorific value has recently become of concern. Blanched raw peanut kernels contain about 46 to 50% fat accounting for 70% of their calories. Just 100 g of raw peanuts, or dry roasted peanuts, or peanut butter contains as much as 550 to 600 calories. In this diet conscious world, it is therefore conceivable that low-calorie peanuts retaining their original flavor, aroma and shape would easily replace the higher calorie peanut (or other nut) products if the prices were reasonable. It has also been shown by Pominski et al, J. Ame. Oil Chem. Soc., 41, 66-68 (1964) that low-calorie, partly defatted peanuts have a longer shelf life due to the reduced oil content.
For at least two decades, many efforts have been made to prepare high-quality, low-calorie peanuts by their partial defatting, possibly without a significant loss of shape, aroma, color and organoleptic qualities. One of these approaches has employed extraction with organic solvent(s), notably hexane; another has used mechanical pressing. Some of the problems of the hexane extraction processes include excessive stripping time and high temperature required to remove the last traces of hexane. These factors adversely affect the organoleptic quality of extracted peanuts, and this approach has not gained much commercial acceptance.
A method of mechanical pressing of peanuts was proposed in 1967 by Vix et al, U.S. Pat. No. 3,294,549. Blanched peanuts with a moisture content of about 5% are mechanically pressed to remove 50 to 80% of the oil. The pressed, misshapen peanuts are then submerged into hot water to expand them back to their original size and shape. The expanded peanuts must then be dried to achieve reasonable shelf life. This process, however, causes considerable splitting (12 to 43%) and breakage (3.6 to 46%) of peanuts. Also, the soaking of pressed defatted peanuts in hot water resulted in a loss of about 5% of the water solubles, mainly sugars and proteins.
Wilkins et al, U.S. Pat. No. 4,466,987, discloses a process for preparing low fat nuts, such as peanuts, wherein the nuts are initially moistened and then roasted prior to pressing them to remove a limited amount of the oil. The pressed nuts are then hydrated to cause them to reconstitute approximately to their normal shape during a final roasting.
Roselius et al, U.S. Pat. No. 4,328,255, teaches a method of extracting coffee oil containing aromatic constituents in high yield and in stable form by extracting solid, roasted coffee with dry carbon dioxide under supercritical conditions of temperature and pressure.
Other investigators have used supercritical fluid extraction (SCFE) processes essentially to extract oil from oilseeds, e.g. soybeans, rapeseed/canola oil corn germ and sunflower. However, since the extraction of oil was the main goal of such work, the oil seeds were cut, flaked, cracked and/or ground to increase the rate of oil extraction.
It was the goal of these authors to develop a process for defatting peanuts, and conceivably other nuts, at least partially while keeping the kernels intact as far as possible. Of course, the disadvantages related to the hexane (or another organic solvent) extraction were to be avoided, and the organoleptic qualities of these popular snacks to be maintained to a maximum degree.